Oxidation of alkylaromatic compounds

ABSTRACT

In a process for oxidizing an alkylaromatic compound to the corresponding hydroperoxide, a feed comprising an alkylaromatic compound is contacted with an oxygen-containing gas in the presence of a catalyst comprising a cyclic imide. The contacting is conducted at a temperature of about 90° C. to about 150° C., with the cyclic imide being present in an amount between about 0.05 wt % and about 5 wt % of the alkylaromatic compound in the feed and the catalyst being substantially free of alkali metal compounds. The contacting oxidizes at least part of the alkylaromatic compound in said feed to the corresponding hydroperoxide.

PRIORITY CLAIM

This application is a divisional of and claims priority and benefit ofU.S. application Ser. No. 13/122,608, filed Apr. 5, 2011 (now allowed);International Application No. PCT/US2009/057239, filed Sep. 17, 2009 andU.S. Provisional Application Ser. No. 61/122,452, filed Dec. 15, 2008,the disclosures of which are hereby incorporated by reference in theirentireties.

FIELD

The present invention relates to a process for oxidizing alkylaromaticcompounds and for converting the oxidation product to phenol and thecorresponding ketone.

BACKGROUND

Phenol is an important product in the chemical industry and is usefulin, for example, the production of phenolic resins, bisphenol A,ε-caprolactam, adipic acid, and plasticizers.

Currently, the most common route for the production of phenol is theHock process. This is a three-step process in which the first stepinvolves alkylation of benzene with propylene to produce cumene,followed by oxidation of the cumene to the corresponding hydroperoxideand then cleavage of the hydroperoxide to produce equimolar amounts ofphenol and acetone. However, the world demand for phenol is growing morerapidly than that for acetone. In addition, the cost of propylenerelative to that of butenes is likely to increase, due to a developingshortage of propylene.

Thus, a process that uses butenes or higher alkenes instead of propyleneas feed and coproduces methyl ethyl ketone (MEK) or higher ketones, suchas cyclohexanone, rather than acetone may be an attractive alternativeroute to the production of phenols. For example, there is a growingmarket for MEK, which is useful as a lacquer, a solvent and for dewaxingof lubricating oils. In addition, cyclohexanone is used as an industrialsolvent, as an activator in oxidation reactions and in the production ofadipic acid, cyclohexanone resins, cyclohexanone oxime, caprolactam andnylon 6.

It is known that phenol and MEK can be produced from sec-butylbenzene,in a process where sec-butylbenzene is oxidized to obtainsec-butylbenzene hydroperoxide and the peroxide decomposed to thedesired phenol and methyl ethyl ketone. An overview of such a process isdescribed in pages 113-121 and 261-263 of Process Economics Report No.22B entitled “Phenol”, published by the Stanford Research Institute inDecember 1977.

For example, in our International Patent Publication No. WO06/015826, wehave described a process for producing phenol and methyl ethyl ketone,in which benzene is contacted with a C₄ alkylating agent underalkylation conditions with a catalyst comprising zeolite beta or amolecular sieve having an X-ray diffraction pattern including d-spacingmaxima at 12.4±0.25, 6.9±0.15, 3.57±0.07 and 3.42±0.07 Angstrom toproduce an alkylation effluent comprising sec-butylbenzene. Thesec-butylbenzene is then oxidized to produce a hydroperoxide and thehydroperoxide is decomposed to produce phenol and methyl ethyl ketone.The oxidation step can be conducted with or without a catalyst underconditions including a temperature between about 70° C. and about 200°C., such as about 90° C. to about 130° C., and a pressure of about 0.5to about 10 atmospheres (50 to 1000 kPa). Suitable catalysts are said toinclude the N-hydroxy substituted cyclic imides described in PublishedU.S. Patent Application No. 2003/0083527.

There is a need to find an oxidation process for sec-butylbenzene andcyclohexylbenzene that is highly selective to sec-butylbenzene orcyclohexylbenzene hydroperoxide, that is less sensitive to the presenceof impurities than the existing oxidation processes, and that allowsefficient commercial scale production of phenol and MEK or phenol andcyclohexanone.

It is known from, for example, U.S. Pat. Nos. 6,852,893 and 6,720,462that certain cyclic imides, such as N-hydroxyphthalimide, in combinationwith free radical initiators, such as peroxy compounds or azo compounds,are effective catalysts in the catalytic oxidation of a wide variety ofaliphatic or aromatic hydrocarbons, including alkyl aromatichydrocarbons, such as cumene, cyclohexylbenzene, cyclododecylbenzene andsec-butylbenzene, to the corresponding hydroperoxides. The patents teachthat the oxidation can be conducted over a wide range of processconditions including a temperature of 0 to 500° C. and a molar ratio ofthe catalyst to the hydrocarbon to be oxidized between 10⁻⁶ mol % and 10mol %. However, no suggestion is provided in either patent as to theefficacy, or the preferred conditions, of the process for the selectiveoxidation of sec-butylbenzene to sec-butylbenzene hydroperoxide orcyclohexylbenzene to cyclohexylbenzene hydroperoxide.

U.S. Pat. No. 7,038,089 discloses a process for preparing hydroperoxidesfrom their corresponding hydrocarbons which comprises oxidizing thehydrocarbons, particularly ethylbenzene, at a temperature in the rangebetween 130 and 160° C. with an oxygen containing gas in the presence ofa catalyst comprising a cyclic imide compound and an alkali metalcompound. In particular, the '089 patent teaches that when oxidation ofethylbenzene is carried out in the presence of a catalytic comprising acyclic imide and an alkaline metal compound, simultaneously highreaction rate and high selectivity to the corresponding hydroperoxideare obtained, superior to those which are obtained when both componentsfrom the catalytic system are used independently. In contrast, accordingto the '089 patent, when the cyclic imide alone is used as the catalyst,high imide concentrations have to be avoided for cost and productimpurity reasons, but reducing the imide concentration to tolerablelevels, requires a rise in temperature to increase reaction rate,leading to a decrease of the selectivity to hydroperoxide tounacceptable levels.

According to the present invention, it has now been found that, withsec-butylbenzene and cyclohexylbenzene, oxidation can be conducted atcommercially viable conversion rates and sec-butylbenzene andcyclohexylbenzene hydroperoxide selectivities in the presence of acyclic imide catalyst, without the addition of alkaline metal compound,provided the conversion is conducted over a relatively narrow range oftemperature and cyclic imide concentration. Contrary to the teaching inU.S. Pat. No. 7,038,089, with sec-butylbenzene oxidation andcyclohexylbenzene, it has been found that the presence of an alkalinemetal compound significantly reduces the activity and hydroperoxideselectivity of the oxidation catalyst.

SUMMARY

In one aspect, the present invention resides in a process for oxidizingan alkylaromatic compound to the corresponding alkylaromatichydroperoxide, the process comprising contacting an alkylaromaticcompound of general formula (I):

in which R¹ and R² each independently represents hydrogen or an alkylgroup having from 1 to 4 carbon atoms, provided that R¹ and R² may bejoined to form a cyclic group having from 4 to 10 carbon atoms, saidcyclic group being optionally substituted, and R³ represents hydrogen,one or more alkyl groups having from 1 to 4 carbon atoms or a cyclohexylgroup, with oxygen in the presence of a catalyst comprising a cyclicimide of the general formula (II):

wherein each of R¹ and R² is independently selected from hydrocarbyl andsubstituted hydrocarbyl radicals having 1 to 20 carbon atoms, or fromthe groups SO₃H, NH₂, OH, and NO₂ or from the atoms H, F, Cl, Br, and I,provided that R¹ and R² can be linked to one another via a covalentbond;

-   each of Q¹ and Q² is independently selected from C, CH, CR³;-   each of X and Z is independently selected from C, S, CH₂, N, P and    elements of Group 4 of the Periodic Table;-   Y is O or OH;-   k is 0, 1, or 2;-   l is 0, 1, or 2;-   m is 1 to 3; and-   R³ can be any of the entities listed for R¹; and    wherein said contacting is conducted at a temperature of about    90° C. to about 150° C., said cyclic imide is present in an amount    between about 0.05 wt % and about 5 wt % of the alkylaromatic in    said feed, and said catalyst is substantially free of alkali metal    compounds, said contacting oxidizing at least part of the    alkylaromatic in said feed to the corresponding alkylaromatic    hydroperoxide.

Conveniently, said cyclic imide obeys the general formula (III):

wherein each of R⁷, R⁸, R⁹, and R¹⁰ is independently selected fromhydrocarbyl and substituted hydrocarbyl radicals having 1 to 20 carbonatoms, or from the groups SO₃H, NH₂, OH and NO₂, or from the atoms H, F,Cl, Br and I;

-   each of X and Z is independently selected from C, S, CH₂, N, P and    elements of Group 4 of the Periodic Table;-   Y is O or OH;-   k is 0, 1, or 2; and-   l is 0, 1, or 2.

Conveniently, said alkylaromatic compound of general formula (I) isselected from ethylbenzene, cumene, sec-butylbenzene,p-methyl-sec-butylbenzene, 1,4-diphenylcyclohexane, sec-pentylbenzene,sec-hexylbenzene, cyclopentylbenzene, cyclohexylbenzene andcyclooctylbenzene, with sec-butylbenzene and cyclohexylbenzene beingpreferred.

Conveniently, said contacting is conducted at a temperature of betweenabout 120° C. and about 150° C., such as between about 125° C. and about140° C., and at a pressure between about 15 kPa and about 500 kPa, suchas between 15 kPa to about 150 kPa.

Conveniently, said cyclic imide is present in an amount between about0.05 wt % and about 5 wt % of the alkylaromatic in said feed during saidcontacting.

Conveniently, said contacting converts at least 4 wt % per hour of saidalkylaromatic with a selectivity to the corresponding alkylaromatichydroperoxide of at least 90 wt %.

In one embodiment the process of the invention further comprisesconverting the hydroperoxide into a phenol and an aldehyde or ketone ofthe general formula R¹COCH₂R² (IV) in which R¹ and R² have the samemeaning as in formula (I).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph plotting sec-butylbenzene conversion against time onstream (T.O.S) in the oxidation of sec-butylbenzene at 115° C. withoutN-hydroxyphthalimide (NHPI) according to the process of Example 1 and inthe presence of 0.43 wt % NHPI according to the process of Example 2.

FIG. 1( a) is a graph plotting sec-butylbenzene hydroperoxideselectivity against sec-butylbenzene conversion in the oxidation ofsec-butylbenzene at 115° C. without NHPI according to the process ofExample 1 and in the presence of 0.43 wt % NHPI according to the processof Example 2.

FIG. 2 is a graph plotting reaction rate and sec-butylbenzenehydroperoxide yield against NHPI concentration in the oxidation ofsec-butylbenzene at 115° C. with varying amounts of NHPI according tothe process of Example 3.

FIG. 3 is a graph plotting sec-butylbenzene conversion andsec-butylbenzene hydroperoxide selectivity against NHPI concentration inthe oxidation of sec-butylbenzene at 115° C. with varying amounts ofNHPI according to the process of Example 3.

FIG. 4 is a graph plotting sec-butylbenzene hydroperoxide selectivityagainst sec-butylbenzene conversion in the oxidation of sec-butylbenzeneat 125° C. with varying amounts of NHPI according to the process ofExample 4.

FIGS. 5( a) and (b) are graphs plotting sec-butylbenzene hydroperoxideselectivity against sec-butylbenzene conversion in the oxidation ofsec-butylbenzene at varying temperatures between 115° C. and 150° C. inthe presence of 0.05 wt % NHPI [FIG. 5( a)] and 0.10 wt % NHPI [FIG. 5(b)] according to the process of Example 5.

FIGS. 6( a) and (b) are graphs plotting reaction rate andsec-butylbenzene hydroperoxide selectivity against temperature in theoxidation of sec-butylbenzene in the presence of 0.05 wt % NHPI [FIG. 6(a)] and 0.10 wt % NHPI [FIG. 6( b)] according to the process of Example5.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The terms “group”, “radical”, and “substituent” are used interchangeablyin this document. For purposes of this disclosure, “hydrocarbyl radical”is defined to be a radical, which contains hydrogen atoms and up to 20carbon atoms and which may be linear, branched, or cyclic, and whencyclic, aromatic or non-aromatic. “Substituted hydrocarbyl radicals” areradicals in which at least one hydrogen atom in a hydrocarbyl radicalhas been substituted with at least one functional group or where atleast one non-hydrocarbon atom or group has been inserted within thehydrocarbyl radical.

As used herein, the new numbering scheme for the Periodic Table Groupsis employed as disclosed in Chemical and Engineering News, 63(5), 27(1985).

Described herein is a process for oxidizing an alkylaromatic to thecorresponding hydroperoxide and optionally for cleaving the resultanthydroperoxide produced in (a) to produce phenol and the correspondingketone. The oxidation process comprises contacting a feed comprising analkylaromatic compound to the corresponding alkylaraomtic hydroperoxide,the process comprising contacting an alkylaromatic compound of generalformula (I):

in which R¹ and R² each independently represents hydrogen or an alkylgroup having from 1 to 4 carbon atoms, provided that R¹ and R² may bejoined to form a cyclic group having from 4 to 10 carbon atoms, saidcyclic group being optionally substituted, and R³ represents hydrogen,one or more alkyl groups having from 1 to 4 carbon atoms or a cyclohexylgroup, with oxygen in the presence of a catalyst comprising a cyclicimide of the general formula (II):

wherein each of R¹ and R² is independently selected from hydrocarbyl andsubstituted hydrocarbyl radicals having 1 to 20 carbon atoms, or thegroups SO₃H, NH₂, OH and NO₂, or the atoms H, F, Cl, Br and I, providedthat R¹ and R² can be linked to one another via a covalent bond; each ofQ¹ and Q² is independently selected from C, CH, CR³; each of X and Z isindependently selected from C, S, CH₂, N, P and elements of Group 4 ofthe Periodic Table; Y is O or OH; k is 0, 1, or 2; 1 is 0, 1, or 2; m is1 to 3; and R³ can be any of the entities (radicals, groups, or atoms)listed for R¹. The oxidation is conducted at a temperature of about 90°C. to about 150° C., with the cyclic imide being present in an amountbetween about 0.05 wt % and about 5 wt % of the alkylaromatic in thefeed and the catalyst being substantially free of alkali metalcompounds.

The phrase “provided that R¹ and R² may be joined” and so on is usedherein to mean that, as an alternative to each of R¹ and R² being a(“monovalent”) alkyl group, the two “alkyl” entities designated “R¹” and“R²” are joined into a (“divalent”) hydrocarbyl chain (having 2 to 8carbons in that chain), with respective ends of that “divalent” chainbegin linked to the C atoms specifically shown in formula (I) to form aring. Thus, in an embodiment, R¹ and R² together constitute ahydrocarbyl moiety that connects to the carbon atoms of formula (I) forma cyclic group having from 4 to 10 carbon atoms, conveniently acyclohexyl group, which may be substituted with one or more alkyl grouphaving from 1 to 4 carbon atoms or with one or more phenyl groups.Examples of suitable alkylaromatic compounds are ethylbenzene, cumene,sec-butylbenzene, p-methyl-sec-butylbenzene, 1,4-diphenylcyclohexane,sec-pentylbenzene, sec-hexylbenzene, cyclopentylbenzene,cyclohexylbenzene and cyclooctylbenzene, with sec-butylbenzene andcyclohexylbenzene being preferred. It will also be understood that inthe case where R¹ and R² are joined to form a cyclic group, the numberof carbons forming the cyclic ring is from 4 to 10. However, that ringmay itself carry one or more substituents, such as one or more alkylgroups having from 1 to 4 carbon atoms or one or more phenyl groups, asin the case of 1,4-diphenylcyclohexane.

Sec-butylbenzene Production

In one embodiment, the alkylaromatic compound may be sec-butylbenzenewhich may be produced by alkylating benzene with at least one C₄alkylating agent under alkylation conditions in the presence of aheterogeneous catalyst. The alkylation conditions conveniently include atemperature of from about 60° C. to about 260° C., for example betweenabout 100° C. and about 200° C. The alkylation pressure is conveniently7000 kPa or less, for example from about 1000 to about 3500 kPa. Thealkylation is conveniently carried out at a weight hourly space velocity(WHSV) based on C₄ alkylating agent of between about 0.1 and about 50hr⁻¹, for example between about 1 and about 10 hr⁻¹.

The C₄ alkylating agent conveniently comprises at least one linearbutene, namely butene-1, butene-2 or a mixture thereof. The alkylatingagent can also be an olefinic C₄ hydrocarbon mixture containing linearbutenes, such as can be obtained by steam cracking of ethane, propane,butane, LPG and light naphthas, catalytic cracking of naphthas and otherrefinery feedstocks and by conversion of oxygenates, such as methanol,to lower olefins. For example, the following C₄ hydrocarbon mixtures aregenerally available in any refinery employing steam cracking to produceolefins and are suitable for use as the C₄ alkylating agent: a crudesteam cracked butene stream, Raffinate-1 (the product remaining aftersolvent extraction or hydrogenation to remove butadiene from the crudesteam cracked butene stream) and Raffinate-2 (the product remainingafter removal of butadiene and isobutene from the crude steam crackedbutene stream).

Cyclohexylbenzene Production

In a further practical embodiment, the alkylaromatic compound of generalformula (I) is cyclohexylbenzene and is preferably produced bycontacting benzene with hydrogen in the presence of a heterogeneousbifunctional catalyst which comprises at least one metal havinghydrogenation activity, typically selected from the group consisting ofpalladium, ruthenium, nickel and cobalt, and a crystalline inorganicoxide material having alkylation activity, typically at least onemolecular sieve of the MCM-22 family (as defined below). The contactingstep is conveniently conducted at a temperature of about 50° C. to about350° C. and/or a pressure of about 100 to about 7000 kPa and/or abenzene to hydrogen molar ratio of about 0.01 to about 100 and/or a WHSVof about 0.01 to about 100.

In the case where the alkylaromatic compound that is oxidized accordingto the invention is cyclohexylbenzene, the oxidation product iscyclohexylbenzene hydroperoxide and the cleavage product comprisesphenol and cyclohexanone. The crude cyclohexanone and crude phenol fromthe cleavage step may be subjected to further purification to producepurified cyclohexanone and phenol. A suitable purification processincludes, but is not limited to, a series of distillation towers toseparate the cyclohexanone and phenol from other species. The crude orpurified cyclohexanone may itself be subjected to dehydrogenation inorder to convert it to phenol. Such dehydrogenation may be performed,for example, over a catalyst such as platinum, nickel or palladium.

The alkylation catalyst is conveniently zeolite beta, which is describedin detail in U.S. Pat. No. 3,308,069, or more preferably is at leastone molecular sieve of the MCM-22 family. As used herein, the term“MCM-22 family material” (or “material of the MCM-22 family” or“molecular sieve of the MCM-22 family” or “MCM-22 family zeolite”),includes one or more of:

-   -   molecular sieves made from a common first degree crystalline        building block unit cell, which unit cell has the MWW framework        topology. (A unit cell is a spatial arrangement of atoms which        if tiled in three-dimensional space describes the crystal        structure. Such crystal structures are discussed in the “Atlas        of Zeolite Framework Types”, Fifth edition, 2001, the entire        content of which is incorporated as reference);    -   molecular sieves made from a common second degree building        block, being a 2-dimensional tiling of such MWW framework        topology unit cells, forming a monolayer of one unit cell        thickness, preferably one c-unit cell thickness;    -   molecular sieves made from common second degree building blocks,        being layers of one or more than one unit cell thickness,        wherein the layer of more than one unit cell thickness is made        from stacking, packing, or binding at least two monolayers of        one unit cell thickness. The stacking of such second degree        building blocks can be in a regular fashion, an irregular        fashion, a random fashion, or any combination thereof; and    -   molecular sieves made by any regular or random 2-dimensional or        3-dimensional combination of unit cells having the MWW framework        topology.

Molecular sieves of the MCM-22 family include those molecular sieveshaving an X-ray diffraction pattern including d-spacing maxima at12.4±0.25, 6.9±0.15, 3.57±0.07 and 3.42±0.07 Angstrom. The X-raydiffraction data used to characterize the material are obtained bystandard techniques such as using the K-alpha doublet of copper asincident radiation and a diffractometer equipped with a scintillationcounter and associated computer as the collection system.

Materials of the MCM-22 family include MCM-22 (described in U.S. Pat.No. 4,954,325), PSH-3 (described in U.S. Pat. No. 4,439,409), SSZ-25(described in U.S. Pat. No. 4,826,667), ERB-1 (described in EuropeanPatent No. 0293032), ITQ-1 (described in U.S. Pat. No. 6,077,498), ITQ-2(described in International Patent Publication No. WO97/17290), MCM-36(described in U.S. Pat. No. 5,250,277), MCM-49 (described in U.S. Pat.No. 5,236,575), MCM-56 (described in U.S. Pat. No. 5,362,697), UZM-8(described in U.S. Pat. No. 6,756,030), and mixtures thereof. Molecularsieves of the MCM-22 family are preferred as the alkylation catalystsince they have been found to be highly selective to the production ofsec-butylbenzene, as compared with the other butylbenzene isomers.Preferably, the molecular sieve is selected from (a) MCM-49, (b) MCM-56and (c) isotypes of MCM-49 and MCM-56, such as ITQ-2.

Oxidation Process

The oxidation step in the present process is accomplished by contactinga feed comprising an alkylaromatic compound such as sec-butylbenzene andcyclohexylbenzene with an oxygen-containing gas in the presence of acatalyst comprising a cyclic imide of the general formula (II):

wherein each of R¹ and R² is independently selected from hydrocarbyl andsubstituted hydrocarbyl radicals having 1 to 20 carbon atoms, or thegroups SO₃H, NH₂, OH and NO₂, or the atoms H, F, Cl, Br and I providedthat R¹ and R² can be linked to one another via a covalent bond; each ofQ¹ and Q² is independently selected from C, CH, CR³; each of X and Z isindependently selected from C, S, CH₂, N, P and elements of Group 4 ofthe Periodic Table; Y is O or OH; k is 0, 1, or 2; 1 is 0, 1, or 2; m is1 to 3 such as 1, 2 or 3, and R³ can be any of the entities (radicals,groups, or atoms) listed for R¹. Conveniently, each of R¹ and R² isindependently selected from aliphatic alkoxy or aromatic alkoxyradicals, carboxyl radicals, alkoxy-carbonyl radicals and hydrocarbonradicals, each of which radicals has 1 to 20 carbon atoms.

Generally, the cyclic imide employed as the oxidation catalyst obeys thegeneral formula (III)

wherein each of R⁷, R⁸, R⁹, and R¹⁰ is independently selected fromhydrocarbyl and substituted hydrocarbyl radicals having 1 to 20 carbonatoms, or the groups SO₃H, NH₂, OH and NO₂, or the atoms H, F, Cl, Brand I; each of X and Z is independently selected from C, S, CH₂, N, Pand elements of Group 4 of the Periodic Table; Y is O or OH; k is 0, 1,or 2, and 1 is 0, 1, or 2. Conveniently, each of R⁷, R⁸, R⁹, and R¹⁰ isindependently selected from aliphatic alkoxy or aromatic alkoxyradicals, carboxyl radicals, alkoxy-carbonyl radicals and hydrocarbonradicals, each of which radicals has 1 to 20 carbon atoms.

In one practical embodiment, the cyclic imide catalyst comprisesN-hydroxyphthalimide.

The cyclic imide catalyst is added to the oxidation feed in an amountbetween about 0.05 wt % and about 5 wt %, generally between about 0.1 wt% and about 1 wt %, of the alkylaromatic in said feed. Furthermore, thecyclic imide catalyst may be added to the oxidation feed in an amountbetween (i) about 0.05 and about 0.10 wt %; (ii) about 0.1 wt % andabout 0.2 wt %; (iii) about 0.2 wt % and about 0.3 wt %; (iv) about 0.3wt % and about 0.4 wt %; (v) about 0.4 wt % and about 0.5 wt %; (vi)about 0.1 wt % and about 0.5 wt %, and (vii) about 0.1 wt % to 0.3 wt %of the alkylaromatic compound in said feed. Moreover, the oxidation isconducted in the substantial absence (less than 0.00001% by weight ofthe oxidation reaction mixture) of alkali metal compounds.

The oxidation step is conducted at relatively high temperature ofbetween about 90° C. and about 150° C., such as between about 120° C.and about 150° C., for example between about 125° C. and about 140° C.,since it is found that, with alkylaromatic compound oxidation in thepresence of N-hydroxyphthalimide, the hydroperoxide selectivity againstconversion reaction profile is not affected by increasing thetemperature. The oxidation step is conveniently carried out at apressure between about 15 kPa and about 500 kPa, such as between 15 kPato about 150 kPa. By controlling the cyclic imide catalyst concentrationand oxidation temperature as described herein, it is found that saidalkylaromatic compound conversion rates of at least 4 wt % per hour canbe achieved with a selectivity to the corresponding hydroperoxide of atleast 90 wt %.

Production of Phenol

The hydroperoxide produced by the present oxidation process can beconverted by acid cleavage to phenol and the corresponding ketone. Thephenol can of course then be reacted with acetone to produce bisphenolA, a precursor in the production of polycarbonates and epoxy resins.

The hydroperoxide cleavage reaction is conveniently effected bycontacting the hydroperoxide with a catalyst in the liquid phase at atemperature of about 20° C. to about 150° C., such as about 40° C. toabout 120° C., and/or a pressure of about 50 to about 2500 kPa, such asabout 100 to about 1000 kPa and/or a liquid hourly space velocity (LHSV)based on the hydroperoxide of about 0.1 to about 100 hr⁻¹, preferablyabout 1 to about 50 hr⁻¹. The hydroperoxide is preferably diluted in anorganic solvent inert to the cleavage reaction, such as methyl ethylketone, cyclohexanone, phenol, sec-butylbenzene or cyclohexylbenzene, toassist in heat removal. The cleavage reaction is conveniently conductedin a catalytic distillation unit.

The catalyst employed in the cleavage step can be a homogeneous catalystor a heterogeneous catalyst.

Suitable homogeneous cleavage catalysts include sulfuric acid,perchloric acid, phosphoric acid, hydrochloric acid andp-toluenesulfonic acid. Ferric chloride, boron trifluoride, sulfurdioxide and sulfur trioxide are also effective homogeneous cleavagecatalysts. The preferred homogeneous cleavage catalyst is sulfuric acid.

A suitable heterogeneous catalyst for use in the cleavage of thehydroperoxide includes a smectite clay, such as an acidicmontmorillonite silica-alumina clay, as described in U.S. Pat. No.4,870,217 (Texaco), the entire disclosure of which is incorporatedherein by reference.

The invention will now be more particularly described with reference tothe following non-limiting Examples.

EXAMPLE 1 SBB Oxidation without NHPI

150 gm of sec-butylbenzene (SBB) supplied by TCI America was weighedinto a 300 ml Parr reactor fitted with a stirrer, thermocouple, gasinlet, sampling port and a condenser containing a Dean Stark trap forwater removal. The reactor and contents were stirred at 700 rpm andsparged with nitrogen at a flow rate of 250 cc/minute for 5 minutes. Thereactor was then pressurized with nitrogen to 690 kPag (100 psig) whilemaintained under a nitrogen sparge and was then heated to 115° C. Whenthe reaction temperature was reached, the gas was switched from nitrogento air and the reactor was sparged with air at 250 cc/minute for 6hours. Samples were taken hourly and analyzed by gas chromatography.After 6 hours, the gas was switched back to nitrogen and the heat wasturned off. When the reactor had cooled, it was depressurized and thecontents removed. The conversion results are shown in FIG. 1, and theselectivity results plotted against the conversion results are shown inFIG. 1( a).

EXAMPLE 2 SBB Oxidation in the Presence of NHPI

The process of Example 1 was repeated but with 0.64 gm (0.43 wt %) ofN-hydroxyphthalimide (NHPI) being weighed into the Parr reactor with the150 gm of sec-butylbenzene (SBB). Again the conversion results are shownin FIG. 1, and the selectivity results are shown in FIG. 1( a), fromwhich it will be seen that addition of the NHPI dramatically improvedthe SBB conversion level. The addition of the NHPI also improved theselectivity to sec-butylbenzene hydroperoxide (SBBHP) based onequivalent conversion levels.

EXAMPLE 3 SBB Oxidation at Different Levels of NHPI

The procedure of Example 2 was repeated with the addition of differentamounts of NHPI, namely 0.05, 0.125, 0.215 and 0.43 wt %. The resultsare plotted in FIGS. 2 and 3 and show the impact of NHPI concentrationon reaction rate and sec-butylbenzene hydroperoxide yield (the productof SBB conversion and SBBHP selectivity). The data show that theselectivity to the SBB hydroperoxide is flat at different yields andNHPI content.

EXAMPLE 4 SBB Oxidation at Different NHPI Concentrations and Temperatureof 125° C.

The procedure of Example 3 was repeated with the addition of NHPI inamounts of 0.05, 0.215 and 0.43 wt % and with the reaction temperatureincreased to 125° C. The results are plotted in FIG. 4 and show that at125° C. the hydroperoxide selectivity and the SBB conversion aresignificantly affected by increasing the NHPI concentration. At higherNHPI concentration, higher selectivities are achieved at the sameconversion level.

EXAMPLE 5 SBB Oxidation at Different Temperature and NHPI Concentrationsof 0.05 and 0.10 wt %

The procedure of Example 3 was repeated with the addition of NHPI inamounts of 0.05 and 0.10 wt % and with the reaction temperature beingvaried between 115° C. and 150° C. The results are plotted in FIGS. 5and 6 and show at these NHPI concentrations varying the temperaturebetween 115 and 125° C. has no impact on the selectivity againstconversion profile.

While the present invention has been described and illustrated byreference to particular embodiments, those of ordinary skill in the artwill appreciate that the invention lends itself to variations notnecessarily illustrated herein. For this reason, then, reference shouldbe made solely to the appended claims for purposes of determining thetrue scope of the present invention.

The invention claimed is:
 1. A process for oxidizing an alkylaromaticcompound to the corresponding alkylaromatic hydroperoxide, the processcomprising contacting an alkylaromatic compound of general formula (I):

in which R³ represents hydrogen, one or more alkyl groups having from 1to 4 carbon atoms or a cyclohexyl group, with air in the presence of acatalyst comprising a cyclic imide of the general formula (II):

wherein each of R¹ and R² is independently selected from hydrocarbyl andsubstituted hydrocarbyl radicals having 1 to 20 carbon atoms, or fromthe groups SO₃H, NH₂, OH, and NO₂ or from the atoms H, F, Cl, Br, and I,provided that R¹ and R² can be linked to one another via a covalentbond; each of Q¹ and Q² is independently selected from C, CH, CR³; eachof X and Z is independently selected from C, S, CH₂, N, P and elementsof Group 4 of the Periodic Table; Y is O or OH; k is 0, 1, or 2; 1 is 0,1, or 2; m is 1 to 3; and R³ can be any of the entities listed for R¹;and wherein said contacting is conducted at a temperature of about 90°C. to about 150° C. and a pressure of between about 15 kPa and about 500kPa, said cyclic imide is present in an amount between about 0.05 wt %and about 5 wt % of the alkylaromatic compound in said feed, and saidcatalyst is substantially free of alkali metal compounds, saidcontacting oxidizing at least part of the alkylaromatic compound in saidfeed to the corresponding alkylaromatic hydroperoxide.
 2. The process ofclaim 1, wherein said cyclic imide obeys the general formula (II):

wherein each of R⁷, R⁸, R⁹, and R¹⁰ is independently selected fromhydrocarbyl and substituted hydrocarbyl radicals having 1 to 20 carbonatoms, or from the groups SO₃H, NH₂, OH, and NO₂ or from the atoms H, F,Cl, Br, and I, each of X and Z is independently selected from C, S, CH₂,N, P and elements of Group 4 of the Periodic Table; Y is O or OH, k is0, 1, or 2, and 1 is 0, 1, or
 2. 3. The process of claim 1, wherein saidcyclic imide comprises N-hydroxyphthalimide.
 4. The process of claim 1,wherein said contacting is conducted at a temperature of between about125° C. and about 140° C. and a pressure of about 15 kPa to about 150kPa.
 5. The process of claim 1, wherein said cyclic imide is present inan amount between about 0.1 wt % and about 1 wt % of the alkylaromaticin said feed during said contacting.
 6. The process of claim 1, whereinsaid cyclic imide is present in an amount between about 0.05 wt % andabout 0.5 wt % of the alkylaromatic in said feed during said contacting.7. The process of claim 1, wherein said contacting converts at least 4wt % per hour conversion of said alkylaromatic compound with aselectivity to the corresponding alkylaromatic hydroperoxide of at least90 wt %.
 8. The process of claim 1, wherein said alkylaromatic compoundis cyclohexylbenzene.
 9. The process of claim 1, further comprising thestep of: cleaving the alkylaromatic hydroperoxide to produce phenol andthe corresponding ketone.
 10. The process of claim 9, wherein thecleaving is conducted in the presence of a catalyst.
 11. The process ofclaim 9, wherein the cleaving is conducted in the presence of ahomogeneous catalyst.
 12. The process of claim 11, wherein saidhomogeneous catalyst comprises at least one of sulfuric acid, perchloricacid, phosphoric acid, hydrochloric acid, p-toluenesulfonic acid, ferricchloride, boron trifluoride, sulfur dioxide and sulfur trioxide.
 13. Theprocess of claim 9, wherein the cleaving is conducted in the presence ofa heterogeneous catalyst.
 14. The process of claim 13, wherein saidheterogeneous catalyst comprises a smectite clay.
 15. The process ofclaim 9, wherein the cleaving is conducted at a temperature of about 40°C. to about 120° C., a pressure of about 100 to about 1000 kPa, and aliquid hourly space velocity (LHSV) based on the hydroperoxide of about1 to about 50 hr⁻¹.
 16. The process of claim 1, wherein the air issubjected to water removal.